Default node size for mkfs.btrfs is 16kB and offers best performance. If file is small enough to be stored in btrfs leaf metadata it is directly stored in metadatas (max file size if 16384-148 heaf header)
Disable COW on /tmp: sudo chattr -R +C /tmp
Depending on your chosen Linux distribution, you might want to follow the latest 5.10 LTS
kernel which is supposed to contain numerous btrfs related improvements. However, be warned
that the current 5.10 kernel also has several btrfs related performance regression issues so
definitely do not rush to upgrade even if you are capable of doing so.